Multiplex telegraph system



y 4, 1950 w. H. BLISS MULTIPLEX TELEGRAPH sysm 4 Sheets-Sheet 1 Filed March 28; 1945 M/lT/Pti flaw/v6 INVENZIOR.

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July 4, 1950 w. H. BLISS MULTIPLE TELEGRAPH SYSTEM Filed March 28; 1945- INVENTOR Wi/PPEA/ A4 54 us BY /l77'0i/V7I 4 Shasta-Sheet 5 G a u. E Q Q v i Q us. lad a: g

C 3 JL Patented July 4, 1950 MULTIPLEX TELEGRAPH :SYS TEM "Warren -H. "Bliss, 'Riverhe'ad, N. Y,., a'ssignor to Radio'Corporation of America, a corporation of' Delaware Application March 28, 1945, Serial No. 585,344

"10Claims. l

The present invention relates to a multiplex telegraph system in which the intelligence is conveyedby a frequency shift keying procedure, and channel phasing (assignment of'different channels to the common (path) is accomplished automatically by means Tof-.a'synchronizing component of the transmittedsignal.

An important advantage of the present invention lies in thecomplete elimination of the usual .mechanical or electronic channe1 selecting distributors customarily employed in multiplex systems. Channeling isperformedin the'system'of the present invention by synchronized gating circuits, and the operationof each channel is .-made to be entirely independent of the others.

Another advantage of the present invention .lies in the high degree of flexibility ofithe system which enables the number of channels, the amount of time alloted to each :channel and the amount of time used'for transmitting the phasing signal to be adjusted to meet varioustransmission speeds and conditions of the transmitting medium.

A further advantage of "the invention over known systems is that a large portion of "the receiving end equipment 'is identical with that at the sending end. From'a commercial aspect this has many practical values for two-way opera- .tion.

A more detailed description of the invention follows in conjunction with a drawing, in which 'Figs. 1 and Zillustrate, .by way "of example, the sending end and receiving end apparatus, 'respectively, of a complete multiplex telegraph system in accordance withthe invention; Fig. 3 is .aseries of wave forms given in explanation of the operation of the system of Figs. 1 and 2; Fig. 4 shows the circuit details of the frequency shift keyer, the on-ofi keyer and the frequency shift radio telegraph transmitters of Fig. 1; and

Fig. 5 illustrates the circuit details of the limiter and discriminator of Fig. 2.

A specific embodiment of the sending end equipment of the invention is illustrated in Fig. 1. Although a two channel multiplex system is illustrated by way of example, any number of channels up to or 12 may be used.

In Fig. 1, units 2 and 3 are Standard Auto Heads used in telegraph practice to convert perforated .tapecharacters (constituting the intelligence impressed .on an advancing tape) into dots and dashes. The outputs of these units .2.and 3, in the form of thesedots and dash .telegraphlcharacters, are fed. into gate circuits 4 and5. The auto heads may beany suitable automatic telegraph transmitter, suchas the standard Wheat- .stone type or Creed arrangement.

A 60 cycle supply I is used to synchronously drive units 2 and 3iandalso to synchronize pulse unit 11. UnitT is a blocking oscillator or the Hartley type havinga vacuum 'triode 29, a tank circuit composed .of-coil"26 .and condenser2'5, a series plate supply res'istor'3'l, a platefsupply'bypass condenser'28, a grid condenserzl; anda grid leak resistor consistingof three resistors32, 33 and Min se'ries Resistor 33 is variable'for the purpose "of adjustingthe blocking rate. Across resistor "34 is suppliedthe 60 cycle synchronizingvoltage through condensers"35. The pulse output yofblockin oscillator "1 .is taken outthrough'condenser '30 on lead 84' and fed into a multiplephas'ingand gate control "The input portion of unittfi consistsof'three buffer vacuum trio'des' 3| ;''6'!' and 14. The "control grids-of these triodes are all connected'i to lead '84 "from ithei'7blocking oscillator '1 and to ,ground through'acommon resistorl65. The cathodes of'these same 'tri'ode'shave a commont'resister 63 ahdnommonizonden'sertt which islconnected to ground, asshown.

"Trio'de 31 ha's'ra 'p'late'resi'stor '38. Its plate is coupled to -the'grid of vacuum :triode"43 byway of condenserBQ. 'fTriodes 'drand "48 "comprise a Snip-flop circuit (Whichcan be called 'a'self re- "storin -trigger circuit) "with "triode' lli inthenormal' stabilized conduction 'state and tube 43" in a normally.non=conductive"istate.' There are "plate resistors 730 and 4|, 'aresistor 4-4 connecting'the grid of "tube 431with the plate oftube48,..afcondenser "4-5 connecting the plate "of 'tube" 43 with "the grid 'of'tube 48, and a common "c'athodeme- .sistor vM.

riode 43 has a fixed*grid"resistor"42, while 'triodedB has'ta "variable "grid resistor 46.

trigger circuit composedof "gas 'tetr'odes 55 and62.

Gas tetrodes "55 andtZ have plate resistors 5i and 52 and a commutating condenser 53intercnnnecting 'the'plates of these tubes. Tube 52 is normally in a stabilized conducting state and has 'its control grid connected to the plate *of tube 55 through condenser 54 and 'alsoto ground. through fvar'iable resistor "6 l. Tubei55 is normally in anon-conductive state. The screen grid .and cathode of tube?! are connected'lto ground. ITubel55 has a grid resistor 'l'lfl, a cathode resistor 56 and .a screen 'gridnegative "bias their states of conduction, and after an interval of time, depending upon the time constants of the circuit, the conductive states of the two tubes will again revert to their normal conditions.

The rest of the multiple phasing and gate control unit 36 consists of two more chains of flipflop circuits identical with the one just described. They have-input buffer triodes 61 and 14, first flip-flop circuit tubes 68, 10 and 15, 11, respectively, and second flip-flop circuit gas tubes TI,

13 and 18, 86, respectively. Theoutput of tube 1| is fed into gate circuit 4 by way of lead 23., The output of tube 18 is fed into the on-off keyer 82 by way of lead I43.

Unit 4 is a gate circuit consisting of vacuum diodes8 and 9, input resistors I9 and II, output resistor I6 and a battery I1. This gate circuit operates in channel I from standard auto head '2. A second gate circuit 5, identical with unit 4, operates in channel 2 from auto head 3. The

diodes of gates 4 and 5 are conductive in the absence of a positive pulse from either the autoheads 2 and 3 or from leads 23 and 24.

Vacuum diodes 20 and =2I and a common output resistor 22 comprise a circuit for combining the outputs of the gate circuits. These diodes 20 and 2! are conductive only when the two diodes of each of their respective associated gates 5 and 4 are non-conductive.

Unit 83 is a conventional frequency shift radiotelegraph transmitter with a frequency shift keyer unit 8| and an on-off keyer unit 82.

Fig. 2 illustrates the receiving end equipmentf associated with gas tubes 55 and 62 of Fig. 1,

except that the screen grid of tetrode 98 is arranged for variable negative bias from battery I04 through potentiometer I03. The output,

' taken from the cathode of tube 98, is fed through a differentiating condenser I91 and a diode I09 'to a multiple phasing and gate control unit H9 by way of lead I35.

Multiple phasing and gate control unit III] is identical with the upper two circuit portions of unit 36 of the sending end equipment, Fig. 1.

' However, the lower one-third of unit 36, Fig. l,

is not used when this type of circuit is employed at the receiving terminal as illustrated by unit IID, Fig. 2. The outputs of unit III) appear on leads I36 and I31 and are fed into gate circuits 81 and 88.

These gate circuits 81 and 88 are the same asv gate circuits 4 and 5 of the sending end equipment and operate in the same manner. The outputs of the two gate circuits 81 and 88 are fed into pulse regenerators III and H3, respectively. These pulse regenerators are fully described in my patent application entitled Pulse Regenera tor Circuit, Ser. No. 590,822 filed April 28, 1945.

Units I I2 and H4 are conventional telegraph signal recorders, such as the ink slip type.

Fig. 3 consists of a series of wave forms repthe wave forms of the outputs of standard auto heads '2 and 3, respectively, when the character NE is sent on channel I and the character U is sent on channel 2. Wave forms H5 and H6 employ conventional length dot and dash code characters, although it should be understood that the inventon is not limited to dot and dash characters only, since the invention is also applicable to other systems which may employ printers wherein a plurality of equal length units or code characters (baud length) are employed.

Pulse unit 1 operates as a blocking oscillator and a negative voltage pulse is developed across plate resistor 31 for each group of oscillations of the blocking cycle. These pulses are shown as line II1 of Fig. 3.

In order to properly synchronize the outputs of auto heads 2, 3 and pulse 1, they are all connected to a common 60 cycle supply. The pulse frequency of unit 1 is adjusted to the desired value by means of variable resistor 33. Although only one speed of operation for a two channel system is illustrated in this disclosure, it should be understood the invention is capable of providing various speeds and different number of channels.

The gating circuits 4 and 5 serve to select certain parts of the signals from each channel and their outputs are combined to produce a composite signal which is transmitted. In order to operate the gating circuits in the proper manner, the multiple phasing and gate control unit 36 is provided. It consists of three chains or circuit portions each of which has a buffer or input tube, an adjustable delay two-tube element, and an adjustable length two-tube control element.

Referring to Fig. 1, the pulses from unit 1 (line II1 of Fig. 3) are passed through a buffer tube 3|, where the polarity of the pulses is reversed, and applied to the control grid of triode 43. Tube 3i is normally conductive and becomes non-conductive for the duration of the negative pulse applied to its control grid over lead 84. Triodes 43 and 48 are connected in a flip-flop circuit with resenting voltage variations at various points designated hereinafter and illustrates the operation of the invention. Lines H5 and I I6 show tube 48 conductin and tube 43 normally nonconducting in the stable state. The application of a positive pulse from the plate of tube 3| (which occurs when tube 3| becomes non-conductive) to the control grid of tube 43 via condenser 39, causes this tube 43 to become conductive and tube 48 to become non-conductive, in which condition the flip-flop circuit is in the active state. Such action occurs because of the regenerative interconnection between the electrodes of the two tubes.

After each triggering of vacuum tube 43, the second vacuum tube 48 of the trigger circuit 43 recovers its state of conduction as soon as condenser 45 discharges sufficiently through resistor 46 to allow the control grid voltage of tube 48 to rise above the cut-off value. The length of conduction period of tube 43 is thus controlled by the value of resistor 46. With the repeated application of pulses from triode 3i, tube 43 holds conduction during the first portion of each pulse cycle while tube 48 holds conduction during the latter part of each pulse cycle. Wave form II8 of Fig. 3 shows the conduction versus time curve for tube 43. Flip-flop circuit 43, 48 constitutes a pulse delay circuit, in effect.

The output of this two-tube delay circuit is taken from the plate of tube 43, differentiated or peaked by condenser 49, and passed on to the grid of tube 55. 7 It is the terminating or trailing edge of the output pulse from tube 43 which produces *the positive: pulse necessary to trigger or fire tub'e 55. Gas tetrodes 55 and 62- operateto produce-a result similarto tubes 43 and48and the conduction time of tube 55is adjusted: by means of resistor 6|. The output of tube 55, ap-

pearing on lead 24, is given as line I20 of Fig. 3. It should be noted that the time when tube. 55 starts'conduction for each pulse cycleis controlled byresistor 48; the phase of the gate control pulses from tube 55 (line I20) can be set at any desired value with respect to the .main control pulses shown in line II I.

A'similar set of gate control pulses (line I I9) is developedbythe second chain of themultiple phasing and gate control unit v36. These occur on 'leadl23 and their phase differs from thoseon lead'24'as shown by wave forms H9 and I20. This difierence inphase is achieved by using differenttime constants for the second chain trigger circuits than for the first chain.

By. means of gating circuit 4, certain parts of the telegraph signals of channel I from auto head 2 are passed on to the pulse combining unit 6. This is accomplished by the gating action as follows: When no positive voltage is applied to resistors I 8 and I i, point I38 remains at a comparatively low value of potential since resistor I6is several times as large as either of the equal resistors I8 and H. In the presence of this low valuexof potential on point I38, diode 2| of combiner 6 is essentially non-conductive. Application of a positive voltage to the cathode of either diode .8 or 9 alone causes very little effect on the potential of point I36 but the simultaneous. application of positive voltages to the two cathodes causes both diodes to cease conduction; as a result of which point [38 risesin potential to a valueequal to the voltage of battery II. This rise in potential on point I38 is. sufficient to cause diode 2I to conduct for the duration of'the potential application.

Because of the fact that positive pulses must beapplied simultaneously toboth diodes of each gate4- or 5, in order to produce the desired effeet. on the combiner 6, it will beseen that'the gating voltage on lead 23 allows only a portion .ofthe signal from auto head 21in channel't l to be passed on to combining unit 8, as, shownby wave form I22. In a like maner the channel"#2 .wave form! i6 from auto head 3 is gated by wave form. I2Il'onlead 24 to cause diode 28 of combiner; 6 toconduct and give the output of line .123. .It shouldbe noted that each dash in the telegraph code autohead signals in channels #I and #2 appearing inlines H5 and [I6 has been converted to three short spaced pulses (note lines I22'and 128), while eachdot in the auto-head signals in channels #I and #2 has beenconverted to .a single short pulse. 7 p

..Diodes.28.and 2I combine the outputs of gating units 4 and 5 in a common resistor 22. Thiscombined wave form is shown as line I24 and isfed 'into a frequency shift keyer 8!.

Inorderto :transmit a suitable phasing signal thatrmay be used at the receiving terminal to "segregate. the channels, the radio, frequency of the transmitter 83 at the sending point-is keyed on and oii accordingto wave form I2I. Wave formi IZl is produced bythe third chainof the -multiple phasing and .gate control unit 36; namely,electron tubes 74,15, TI, 18, and 80 which function in the samemanner astubes 3|, 43,v 48, '55 and 62, respectively. Thiswave. form.I.2.I is appl'iedfi-to; the. oni-offdreyer 82 'ibyimeans :offilead 6 I43; and this keyer controls the Pradio transmitter'83 in accordance with this wave form.

Wave form I25 illustrates-the general character of the transmitted wave sent out by transmitter83over antenna I44. It consists of gaps causedby the on-oiT keyer 82 and mark and space frequencies are controlled by the frequency shiftkeyerBI. A lower frequency is shown for mark" conditionthan for space condition. By way of example only, the outputfrequencies :for mark-and space conditions might be 7070 kc. and 7071 kc., respectively. An inspection of waveform l2l, I24 and I25 will'show'the' following: Whenever a pulse ocours in the combined signal of wave form I24, simultaneously with a pulse of wave form .I'2 I,ithe transmitter 83 sends out a mark frequency for theduration: only of the pulse in wave form I24. In the intervals betweenpulses in wave form I24 and during the occurrence of the pulses .in wave form I2I, the transmitter 83 sends out a space frequency. During the gaps or intervals between pulses in wave form "I2I there is no radio frequency output from transmitter 83.

At the radio receiving terminal (Fig. 2), the signal is picked up by means of a superlieterodyne radio receiver '85 whose intermediate frequency is taken as the output and fed over leads I45" into an amplitude limiter and frequency discriminator unit 86 and also by Way of lead I45 into'gap synchronizing unit 89. Wave form I25 may also be considered as the general character of the output of receiver 85 asmentioned above. The transmitted wave form from the antenna 144 of'Fig. 1 may,xin general, occur at atleast several megacycles'while the intermediate frequency output of the receiver85 of Fig; 2 may be of the order of several hundred kilocycles.

The limiter and discriminator unit 86 maybe the conventional circuit used in frequency modulation receivers and it serves to convert'the incoming wave form I25 into the form shown by line I26. Wave form I26 has threevalues of levelzcorresponding to mark, space and gap as radiated from the sending point (Fig. 1). The center value of level, corresponding to the gap phasing signal may be disregarded in this wave form I26, as it isnot. used.

However, the gap phasing signal is used directly from wave form I25 by means of synchronizing unit 89. The two gas tetrodes 98'and I05: comprise a self-restoring trigger or flip-flop circuit and function in a manner similar to comparable circuits described in Fig. 1, for example, tubes 55 and 62. Tube I M is normally conducting and tube 98 normally non-conducting. As the incoming signal voltage in lead I45 rises at the termination of each gap, tube 98 is fired or triggered into conduction. The conduction periodof tube 98 is adjusted by means of resistor I39 to be nearly equal to the original pulse period of line I2I. The outputwave form of. tube 98 is shown as line I21 (Fig. 3), which correspondsto Wave. form I2l.

Potentiometer I03 supplies an adjustable-bias control to the screen grid of tube 98' and this bias operates as an input signal threshold control in order to prevent false triggering of tubesfl by noise pulses occurring in the signal synchronizing gap. Putting it in other Words, the rise in potential. on" lead I46 necessaryto operate tube 98] must exceed a predetermined valuev determined by the bias control on the screengridi of tube as. 1

A differentiating condenser I 01 and resistor I08 convertwave form I2'I into wave form I28. and diode I09 passes the negative pulses of this wave form on to a multiple phasing and gate control unit H0. Unit IIO performs in exactly the same manner as the corresponding unit 38 in Fig. 1 and its two outputs appearing on leads I36 and I3! are as illustrated by lines I29 and 130 of Fig. 3. Actually, unit IIO includes the same circuit elements as the upper two chain circuit portions of unit 36. The third or lower portion of unit 36 in Fig. 1 is omitted from unit H in Fi 2. It should be observed that wave forms I29 and I30 are similar to wave forms [I9 and I20.

. Gating units 87 and 88 also function exactly the same as similar units 4 and 5 at the sending and except that they separate the signals for each channel from the composite input signal. For example, the wave form of line I23 is applied via lead I41 to the cathode of diode 90 while the wave form of line I29 is applied via lead I36 to the cathode of diode 9|. The gated output of this unit 81 as it appears on lead I40 is shown by line I3I. This is composed of signals corresponding to those of channel #I.

The wave form of line I26 is also applied via lead I48 to the cathode of diode I90 while the wave form of line I30 is applied via lead I31 to the cathode of diode I9I. Thus similar type signals for channel #2 (line I32) constitute the gatedoutput from gate unit 88.

It should be noted that the gate 81 passes pulses (note wave form I3!) only when pulses occur simultaneously in lead I36 and lead I4! as represented by wave forms 129 and I26. The pulses in wave form I26 must, however, be above the center value to be passed by gate 81. Similarly. gate 88 passes (note wave form I32) only when pulses occur simultaneously in lead I37 and lead I48 as represented by wave forms I30 and I26. The pulses in wave form I26 must, however, be above the center value.

Pulse regenerators III and H3 are used to elongate (reconstruct or rebuild) the pulse type signals of lines I3I and I32 into full bodied dots and dashes as shown by iines I33 and I34, respectively. These pulse regenerators are preferably of the type disclosed in my copending application Serial No. 590,822, filed April 28, 1945.

The received signals for the two channels may be registered on any type of a telegraph recorder such as the ink slip type indicated as units H2 and H4.

The illustrative wave forms of Fig. 3 show that the fundamental pulse period (pulses of line H1) is divided into three parts as portrayed by the transmitted wave form I25. This is for a two channel multiplex system. The relative lengths of nel #1 portion and channel #2 portion) may be proportioned in any desired manner as propagation conditions and practice may warrant. This is accomplished by appropriate adjustment of variable registors 46, BI, 39, 12, I6 and IQ of multiple phasing and control unit 36 of the sending end equipment, Fig. 1, and by similar elements in the multiple phasing unit H0 at the receiving end.

For a three channel multiplex, a fourth chain of electron tubes, (such as tubes 3], 43, 48, 55 and 62, Fig. 1), would be included in the multiple phasing and gate'control unit 36 and a third gate circuit like unit 4 or 5 would be needed. Also these three parts (gap portion, chansimilar additional items would be used at the receiving terminal. The fundamental pulse peri 0d would then be divided suitably into four parts insteadof three, as previously explained. Obviously, the invention may be made to operate with any desired number of channels.

In Fig. 4 there are shown the circuit details of the boxes (H, 82 and 83 of Fig. 1, corresponding to the frequency shift keyer, the on-ofi keyer and the frequency shift radio telegraph transmitter. In the frequency shift transmitter, the shift in frequency is accomplished by switching a small condenser 200 in parallel with the quartz crystal 20I. A relay 202 is shown as a means whereby mark and space signals may be used to produce frequency shifts comparable thereto. The ire:- quency shift keyer 8| illustrates a simple means for using the output of combiner 6 (Fig, 1) to operate the relay 202. The on-off keyer 82 utilizes the potential variation on lead I43 to key the transmitter. Two vacuum triodes 203 and 204 operate in an Eccles-Jordon trigger circuit with a plate potential supply source having its positive terminal at ground potential. The output is taken from the anode of tube 204 and is applied via lead C as control grid bias for amplifier triode 205 in the transmitter. For the gap or off intervals the bias applied to tube 205 is sufficiently negative to block the transmission of radio frequency signals from the oscillator section to the power amplifier. Fig. 5 shows conventional details of a limiter and discriminator which might be used for box 85 in Fig. 2. These details are well known in the frequency modulation art and are not being claimed per se. What is claimed is:

1. A radio telegraph multi-channel system inwhich the conventional length code characters in each channel are converted into one or more spaced pulses of constant amplitude but appreciably shorter in duration than said code characters, comprising a plurality of sources of conventional length telegraph code signals corresponding in number to the number of channels in the system, a phasing circuit for sequentially assigning portions of the signals from said sources to a common radio frequency transmitter, means for assuring synchronism in the operation of said sources of signals and said phasing circuit, said phasing circuit including n+l chain circuits wherein it corresponds in number to the number of said signal sources, means supplying recurring waves to said chain circuits, said chain circuits each including a pair of self-restoring trigger circuits operating in cascade, the trigger circuits in the different chains having different time. constants and having such values that the outputs from the difierent chains constitute phase displaced pulses whose durations are shorter than the code characters from said signal sources, a gate circuit individual to each channel and located between the output of the signal source for each channel and said common radio frequency transmitter, connections from the different out,- puts of said chain circuits to different gate circuits, there being one connection from the outputof each chain circuit to a single gate circuit, each of said gate circuits being so constructed and arranged that it operates to pass a pulse only during the simultaneous occurrence of a telegraph code character from its associated signal source and a pulse from the chain connected to it, as a result of which the duration of the pulse 9 passed'by the gate circuit is limited by the. duration of the" pulse obtained from its associated chain circuit, means for combining the outputs of said gate circuits to form a composite signal coming a plurality of sources of conventional length telegraph :code. signals corresponding in number to'the number of channels in the system, a phas= ing circuit for sequentially assigning portions of the signals from said sources to a common radio frequency shift transmitter, ,a source of low audio irequency'current for assuring'synchronism in the'operation of said sources of signals and said phasing circuit, said phasing circuitinclu'clinga plurality of chain circuits corre-' sponding in number to the number of said signal sources, means supplying recurring Waves to said, chain circuits, said chain circuits each including a pair of self-restoring trigger circuits operating in cascade, the trigger circuits in the different chains having diii'erent time constants and havingsuch. values that the outputs from the different chains constitute phase displaced pulses Whose durations are shorter than the code characters from said signal sources, a gate circuit individual to each channel andlocated between the output of the signal source for each channel-and said common radio frequency transmitter, connections from the different outputs of said chain circuits to diiferentgate circuits; there being oneconnection from-the output of each chain circuit to a single gate circuit, eachof said gate circuits being so constructed and arranged that it operates to pass a pulse onl during the simultaneous occurrence of a telegraph code character from' its associated signal source and a pulse from-the chain connected to it, as a result of which the duration of the pulse passed by the gate circuit is limited by the. duration of the pulse obtained from its associated chain circuits, means for combining the outputs of said gate circuits to form a composite signal composedof pulses obtained from the different gate circuits, a frequency shift keyer, controlling said radio frequency transmitter in response to said composite signal, an on-oif keyer. also controlling said radio frequency transmitter, said phasing circuit including still another chain circuit similar in construction and operation to-said first chain circuits and Whose output is connected to said on-off keyer.

3. A radio telegraph multi-channel system in which the conventional length code characters in each channel are converted into one or more spaced pulses of constant amplitude but appreciably shorter in duration than said code characters, comprising a plurality of sources of conventional length telegraphcode signals corresponding in number to the number of channels in the system, a phasing circuit for sequentially assigning. portions of the signals from said sources to a common radio frequency transmitter, means for assuring synchronism in the operation of said sources of signals and said phasing circuit, said phasing circuit including n-f-i chain circuits wherein n corresponds in number t the number of said signal sources, means supplying recurring,

waves to said chain circuits, said chain circuits each including a self-restoring trigger circuit;

the trigger; circuits in the different chains having difierent time constants and having such values that the'outputs from the diiierent chains constitute; phasedisplagzed pulses whose durations are shorter than the code characters from said signal sources, a gate circuit individual to each channel and locatedbetween the output of the signal source for each channel and-said common radio frequency transmitter, connections from'the different outputs of said chain circuits to differentgate circuits, there being one connection from the output of each chain circuit to asingle gate circuit, each. of said .gate circuits being so con structedandarranged'that it operates to passapulse" only during the simultaneous Occurrence of'a telegraph code "character from its associated signal source and a pulse from the chain connected to it, as a result of which the duration of the pulsepassed by the gate circuit is limited by the durationof the pulse obtained from'its associat ed chain circuit, means for combining the out-1 putsofsaid gate, circuits to form a composite signal composed of pulses obtained from the different gate; circuits, means for passing a signal representative of, said composite signal to said radio frequency transmitter, and means for keying said transmitteron and 01? at a rate which is thezsame as the pulse rate in one of said chains.

4; A system inaccordance with claim 1, characterized in this? thatthe chain circuit comprises, a vacuum tube; trigger circuit controlling the firing: of agaseoustube trigger circuit,-eachof said, trigger circuits including two interconnected mul ti-electrode structures;

v'5. A'radimtelegraph multi-channel system'in; Whichthe. conventional length code characters ini'eachchannelare converted. into one or more spaced, pulses of constant amplitude but appreciably: shorter in duration than said code charac- 7 p ng'aplurality of'sources of conventional length telegraph code signals corresponding inrnumber to the-number of'channels inthe system, a phasing circuit for sequentially assign ing portions of the signals from said sources to a common radio frequency transmitter, means for assuring synchronism in the operation of said sourcestpf signal and said phasingcircuit, said; phasing circuit including n+1 chain circuits,

wherein ncorresponds in number to the number oftsaid signal sources, means coupled to said chain circuits" for supplying recurring Waves thereto, said -=chain circuitseach including a pair of self+restoring itriggercircuits operating in cas cade, the trigger circuits. in the different chains having; different-time constants and having such values that the outputs from the differentchains constitute phase displaced pulses whose durations, are shorter than the code characters from said, signal sources, a gate circuit individual to each, channel and located between the output of the; signal source for-each channel and said common radio frequency transmitter, connections from. the different outputs; of said chain circuits to;

difierentgate circuits, therebeing one connectionfrom the output of each chain circuit to a: single gate circuit, each of saidgate circuits being: so constructed and arranged thatit operg; ates to pass a pulse only during the simultaneous;

occurrence of a telegraph code character from its associated signal source and a pulse from the chain connected to it, as a result of which the duration of the pulse passed by the gate circuit bining the is limited by the duration of the pulse obtained 1 ceiving and signal regenerating apparatus comprising a superheterodyne receiver, a plurality of gate circuits coupled in common to the output of said superhetrodyne receiver and similar in construction and operation to the gate circuits at the transmitter end of the system, a phasing circuit under control of the output of said superheterodynereceiver and including chain circuits similar in construction and operation to the chain circuits of the phasing circuit at the transmitter and, the number of chains in the phasing circuit at the receiver end of the system and the number of gate circuits at the receiver end of the-system being the same as the number of channels in said system, there being a gate circuit for each channel, and a signal regenerator in the output or each gate circuit for rebuilding the signals passed by each gate to the longer conventional duration signal code characters.

6. In a radio telegraph. multi-channel system, a plurality of channels each having a source of signals of conventional length code characters, a

pulses obtained gate or shutter arrangement in circuit with each channel and having associated therewith means for passing only a portion of each code character signal, said gates providing phase displaced output pulses of shorter duration than the duration of the code characters, and means for combining the outputs of the gates into a composite signal, said last means comprising a plurality of rectifiers corresponding in number to said channels, each of said rectifiers including an anode, individual connections from said anodes to said gates, a common cathode resistor for said rectifiers and a radio frequency output circuit coupled to said cathode resistor.

7 In a radio telegraph multiplex system, a plurality of channels each having a source of signals of conventional length code characters, an electron discharge device circuit associated with each channel for passing only a portion of each code character signal in the channel, said electron discharge device circuits providing phase displaced output pulses of shorter duration than the code characters, means for combining the outputs of said electron discharge device circuits into a compositesignal, said last means including a plurality of rectifiers corresponding in number to said channels, each of said rectifiers including an anode, individual connections from said anodes to said electron discharge device circuits, a. common cathode impedance element for said rectifiers, a

keying circuit coupled across said common cathode impedance element and controlled b said composite signal, and a radio transmitter coupled to and controlled by said keyer.

8. A system as defined in claim 7, characterized in thisthat said keyer is a frequency shift keyer, and said transmitter sends out different mark and space frequencies in accordance with the operation of said keyer.

12 9. In a radio telegraph multiplex system, wherein spaced pulses in the form of radio frequency energy of different frequencies are respectively transmitted for marking and spacing conditions, receiving and signal regenerating apas the received pulses but of a duration substantially equal to the spaces between the received pulses, a multiple phasing circuit coupled to the output of said synchronizing generator for supplying a multiplicity of phase displaced pulse trains corresponding in number to the number of channels in said system, a plurality of electron discharge device gate or shutter arrangements corresponding in number to the number of channels in said system coupled to the output of said I limiter and discriminator, connections from said phasing circuit to different gates for supplying said gates with different phase displaced pulse trains, each of said gates operating to pass a pulse only during the simultaneous application thereto of both a signal from said limiter and discriminator and a pulse from said phasing circuit,-

and a pulse regenerator coupled to the output of each gate for rebuilding the pulses impressed thereon to longer duration code characters.

10. A system as defined in claim 9, wherein each gate comprises a pair of diodes each of which has an anode and a cathode, a direct connection between said anodes, a common output resistor for said anodes, a source of anode polarizing potential in series with said output resistor, individual cathode resistors for said diodes, a connection from the cathode of one diode to said limiter and discriminator, and a connection fro-m the cathode of the other diode to said phasing circuit.

' WARREN H. BLISS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,189,070 Dietz June 27, 1916 1,194,820 Colpitts Aug. 15, 1916 1,744,711 Von Arco Jan. 21, 1930 1,979,484 Mathes Nov. 6, 1934 1,988,097 Von Arc-o Jan. 15, 1935 2,025,190 Beverage Dec. 24, 1935 2,048,081 Riggs July 21, 1936 2,070,418 Beverage Feb. 9, 1937 2,158,285 Koch May 16, 1939 2,172,354 Blumlein Sept. 12, 1939 2,262,838 Deloraine et al. Nov. 18, 1941 2,324,314 Michel July 13, 1943 2,352,634 Hull July 4, 1944 2,369,662 Deloraine et a1 Feb. 20, 1945 2,376,395 Skellett May 22, 1945 2,428,366 Gillman Oct. 7, 1947 Chatterjea et a1 Oct. 28, 1947 

